The queen clears the way for the rook to occupy the c-file, but as the game continues, it will be poorly-placed on the kingside.
13... a8c8 With the pieces well-developed and the center closed, Black has managed to equalize the game. 14. a1c1  14... c8c1  15. d1c1  15... a7a6 [%c_arrow e2b5;keyPressed;none;from;e2;opacity;0.8;to;b5;persistent;false][%c_highlight b5;keyPressed;none;opacity;0.8;square;b5;persistent;false] Useful to prevent the white bishop from going to b5 in some lines.